There has been known a turnable material handling vehicle such as a hydraulic excavator, wherein a crawler travel system including right and left rotatable crawlers (caterpillars) is employed and this crawler travel system has a crawler frame as a system body.
The crawler frame for a turnable material handling vehicle of this type generally includes a center frame. This center frame has, at its center, a swing bearing with a ring gear for rotatably supporting a revolving frame on which an excavating system (excavating implement), cabin, engine, bonnet and others are mounted; and a right and left pair of track frames coupled to the right and left ends, respectively, of the center frame so as to extend in a back and forth direction. Provided at the front and rear ends of the track frames are idlers and drive wheels around which the crawlers are wound respectively.
In the prior art, for stably sustaining the load of the upper revolving superstructure, four coupling legs formed by sheet-metal welding of a steel plate are provided in total at the four corners of the center frame as a means for coupling the center frame and track frames of the crawler frame. Also, a frame structure is employed which assumes a substantially H-shape or X-shape in plan on the whole.
In the track frame disclosed in Japanese Patent Kokai Publication No. 11-93209 for example, the center frame having a swing bearing at the center thereof is coupled to the track frames with substantially H-shaped coupling legs formed by sheetmetal welding of a steel plate or the like. In the center frame, a central plate section corresponding to a bed plate on which the swing bearing is mounted is supported at the underside thereof by central wall sections (front and rear vertical walls) side wall sections which are formed by bending so as to incline from the central wall sections toward the track frames and a right and left pair of coupling wall sections for coupling the central wall sections to each other. With these wall portions, the load imposed on the swing bearing is directly sustained. An upper coupling plate and a lower coupling plate are welded to the upper and lower ends of these front and rear vertical walls, respectively.
The upper coupling plate is comparatively wide in the back and forth direction and constituted by a flat plate extending to the right and left track frames. Therefore, flying and penetrating mud is likely to adhere to and deposit on the top face of the upper coupling plate as excavating and carrying operation by a construction machine such as a hydraulic excavator proceeds, although the upper coupling plate is more or less inclined toward the right and left track frames.
In the track frame disclosed in Japanese Patent Kokai Publication No. 8-72615, the center frame having a swing bearing at the center thereof is coupled to the track frames with substantially H-shaped coupling legs formed from a steel plate or the like. The member on which the swing bearing is mounted is a round body located at the center of the center frame. The load imposed on the swing bearing is directly sustained by the round body located at the center and four legs extending to the right and left track frames are secured by welding to the round body.
The four legs are formed from appropriate vertical sheet members in order to sustain the load imposed on the swing bearing. Since the top face of each leg is constituted by a flat steel plate relatively moderately inclining toward one of the track frames, flying and penetrating mud is likely to adhere to and deposit on the top face.
In the track frame disclosed in Japanese Patent Kokai Publication No. 2000-230252, the center frame having a swing bearing at the center thereof is coupled to the track frames with substantially X-shaped coupling legs formed by sheet metal welding of a steel plate or the like. In the center frame, the bed plate on which the swing bearing is mounted is supported by right and left side vertical members, a front vertical member and a rear vertical member, and the load imposed on the swing bearing is directly sustained by these vertical members. Covering boards are welded to the upper ends and lower ends of these vertical members thereby forming four legs in a continuous fashion so as to extend to the right and left track frames.
The top face of each leg in this publication is also constituted by a flat steel plate which relatively moderately inclines toward one of the track frames so that flying and penetrating mud is likely to adhere to and deposit on the top face.
In the center frames of the above-cited publications, coupling of the right and left track frames is done by four legs which are formed by sheet metal welding of a steel plate or the like. For this reason, there arises such a problem that the steel plates used for forming the four legs have various shapes and therefore complicated blank layout is involved and the number of members increases.
In addition, many processes such as laying-out, cutting, bending and welding are involved, and many welding places as well as complicated weld lines make the number of welding processes increase, resulting in increased manufacturing time and manufacturing cost.
Further, the center frame has rightwardly extending legs and leftwardly extending legs which are coupled to the right and left track frames and the top faces of these legs are formed from flat steel plates relatively moderately inclining to the track frames, so that mud which flies and penetrates into the center frame during the excavating/revolving-carrying operation of the hydraulic excavator or during traveling of the hydraulic excavator adheres to and deposits on the top faces of the legs in large quantity.
The adhered and deposited mud will penetrate into the swing bearing with a ring gear positioned at the center of the upper part of the center frame and could be a cause of damage to the swing bearing.
Further, the mud which has adhered to and deposited on the legs moves to the top faces of the tracker frames and accumulates there, and this accumulated mud could be an obstacle to the rotation of the upper tracker rollers or a cause of lopsided wear of the upper tracker rollers.
The accumulated mud is removed by washing which, however, needs a lot of water for removal and many washing processes, resulting in increased cleaning cost.
In addition, a large amount of mud is left in the washing site after washing so that the liveries who rent construction machines such as hydraulic excavators have the problem of mud disposal.
The present invention has been directed to overcoming the foregoing problems and a primary object of the invention is therefore to provide a crawler frame for use in a construction machine, which crawler frame can be easily manufactured and easily washed because of less susceptibility to adhesion and deposition of mud.